Glossary of Terms & Definitions
Listed Alphabetically - "E"

EAR: estimated average requirement; a nutrient intake value that is estimated to meet the requirement of  half of the healthy individuals in a particular life stage and gender group.

Echocardiography: a diagnostic test that uses ultrasound to make images of the heart. It can be used to assess the health of the valves and chambers of the heart, as well as to measure cardiac output.

Ectoderm: The primary germ layer that gives rise to the nervous system and the epidermis of skin and its derivatives.

Effector: An organ of the body, either a muscle or a gland, that responds to a motor neuron impulse.

Eicosanoids: Local hormones derived from a 20-carbon fatty acid (arachidonic acid); two important types are prostaglandins and leukotrienes.

Electroencephalogram (EEG): a recording of the electrical activity of the brain, used to diagnose neurological conditions such as seizure disorders (epilepsy).

Electrolytes: Any compound that separates into ions when dissolved in water and is able to conduct electricity;  ionized (dissociated into positive and negative ions) salts in the body fluids. Major electrolytes in the body include sodium, potassium, magnesium, calcium, chloride, bicarbonate, phosphate.

Electron: a stable atomic particle with a negative charge.

Electron transport chain: a group of electron carriers in mitochondria that transport electrons to and from each other in a sequence, in order to generate ATP.

Element: One of the 103 chemical substances that cannot be divided into simpler substances by chemical means. For example, hydrogen, magnesium, lead, and uranium are all chemical elements. Trace elements are chemical elements that are required in very small (trace) amounts in the diet to maintain health. For example, copper, selenium, and iodine are considered trace elements.

Enamel: the hard, white, outermost layer of a tooth.

Endocrine system: the glands and parts of glands that secrete hormones that integrate and control the body's metabolic activity. Endocrine glands include the pituitary, thyroid, parathyroids, adrenals, pancreas, ovaries, and testes.

Enzyme: a biological catalyst. That is, a substance that increases the speed of a chemical reaction without being changed in the overall process. Enzymes are vitally important to the regulation of the chemistry of cells and organisms.

Epidemiologic study: a study examining disease occurrence in a human population.

Epilepsy: also known as seizure disorder. Individuals with epilepsy experience seizures, which are the result of uncontrolled electrical activity in the brain. A seizure may cause a physical convulsion, minor physical signs, thought disturbances, or a combination of symptoms.

Esophagus: a soft muscular tube that connects the throat to the stomach. When a person swallows, the muscular walls of the esophagus contract to push food down into the stomach.

Etiology: the causes or origin of a disease.

Excretion: the elimination of wastes from blood or tissues.

Extracellular fluid (ECF): the volume of body fluid excluding that in cells. ECF includes the fluid in blood vessels (plasma) and fluid between cells (interstitial fluid).